首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6365篇
  免费   189篇
  国内免费   365篇
系统科学   299篇
丛书文集   212篇
教育与普及   243篇
理论与方法论   40篇
现状及发展   65篇
研究方法   48篇
综合类   6012篇
  2024年   57篇
  2023年   102篇
  2022年   154篇
  2021年   181篇
  2020年   126篇
  2019年   61篇
  2018年   84篇
  2017年   107篇
  2016年   107篇
  2015年   185篇
  2014年   267篇
  2013年   235篇
  2012年   266篇
  2011年   294篇
  2010年   275篇
  2009年   285篇
  2008年   333篇
  2007年   327篇
  2006年   243篇
  2005年   253篇
  2004年   173篇
  2003年   177篇
  2002年   223篇
  2001年   214篇
  2000年   192篇
  1999年   295篇
  1998年   214篇
  1997年   210篇
  1996年   174篇
  1995年   206篇
  1994年   176篇
  1993年   157篇
  1992年   132篇
  1991年   97篇
  1990年   101篇
  1989年   79篇
  1988年   72篇
  1987年   36篇
  1986年   21篇
  1985年   8篇
  1984年   3篇
  1981年   2篇
  1980年   2篇
  1979年   3篇
  1978年   2篇
  1974年   1篇
  1973年   1篇
  1972年   3篇
  1970年   1篇
  1969年   1篇
排序方式: 共有6919条查询结果,搜索用时 4 毫秒
81.
运用文献资料、问卷调查、访谈、数理统计和逻辑分析等调查方法,对哈大齐城市群体育社团的发展概况、形成时间、注册情况、体育社团负责人情况、办公场所及活动场地设施情况、组织活动、经费来源渠道等方面的现状进行了详细的调查研究.在此基础上分析哈大齐城市群体育社团发展的优势以及面临的困难和需要解决的问题,并借鉴国内外社团发展经验,提出相应的意见和建议,为体育社团在黑龙江省更好地发展提供理论参考依据.  相似文献   
82.
超高性能混凝土组合桥面板集群化短焊钉抗疲劳特性   总被引:1,自引:1,他引:0  
进行4个单钉和2个群钉疲劳推出试验,将短焊钉疲劳寿命与国内外规范中的焊钉S-N曲线进行比较,并结合塑性损伤有限元模型展开分析。结果表明:短焊钉疲劳破坏表现为根部剪断和周围超高性能混凝土(UHPC)局部压溃;集群化短焊钉疲劳寿命较单钉减少26.9%,在疲劳加载过程中抗剪刚度退化显著快于单钉,当加载次数达到疲劳寿命的12.0%附近时,抗剪刚度比减小至16%左右;AASHTO规范有较大的安全储备,相比之下日本规范(JSCE)与试验结果最为接近,安全富余较少。此外,疲劳荷载下集群化短焊钉根部循环应变幅大于单钉,而且周边UHPC的塑性损伤累积分布更大。  相似文献   
83.
车联网、AR、AI等计算密集、时延敏感型应用迅速发展,而移动设备因自身计算能力相对不足,执行此类应用任务时会因高时延而严重影响用户体验甚至无法满足用户需求。针对此问题,提出综合考虑时延与成本的多用户、多MEC (mobile edge computing)服务器的基站群协作计算卸载模型。并提出基于凸优化的改进烟花算法(improved fireworks algorithm based on convex optimization, CVX-FWA)来对模型进行求解,对用户任务进行合理的卸载与资源分配。仿真结果表明,提出的计算卸载方案有效降低了任务总时延成本值,实现计算卸载资源的整体优化配置。  相似文献   
84.
Reduced hepatic expression levels of bromodomain-containing protein 7 (BRD7) have been suggested to play a role in the development of glucose intolerance in obesity. However, the molecular mechanism by which BRD7 regulates glucose metabolism has remained unclear. Here, we show that BRD7 increases phosphorylation of glycogen synthase kinase 3β (GSK3β) in response to activation of the insulin receptor-signaling pathway shortly after insulin stimulation and the nutrient-sensing pathway after feeding. BRD7 mediates phosphorylation of GSK3β at the Serine 9 residue and this effect on GSK3β occurs even in the absence of AKT activity. Using both in vitro and in vivo models, we further demonstrate that BRD7 mediates phosphorylation of ribosomal protein S6 kinase (S6K) and leads to increased phosphorylation of the eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and, therefore, relieves its inhibition of the eukaryotic translation initiation factor 4E (eIF4E). However, the increase in phosphorylation of 4E-BP1 with BRD7 overexpression is blunted in the absence of AKT activity. In addition, using liver-specific BRD7 knockout (LBKO) mice, we show that BRD7 is required for mTORC1 activity on its downstream molecules. These findings show a novel basis for understanding the molecular dynamics of glucose metabolism and suggest the unique function of BRD7 in the regulation of glucose homeostasis.  相似文献   
85.
86.
The increasing amount of attention paid to longevity risk and funding for old age has created the need for precise mortality models and accurate future mortality forecasts. Orthogonal polynomials have been widely used in technical fields and there have also been applications in mortality modeling. In this paper we adopt a flexible functional form approach using two‐dimensional Legendre orthogonal polynomials to fit and forecast mortality rates. Unlike some of the existing mortality models in the literature, the model we propose does not impose any restrictions on the age, time or cohort structure of the data and thus allows for different model designs for different countries' mortality experience. We conduct an empirical study using male mortality data from a range of developed countries and explore the possibility of using age–time effects to capture cohort effects in the underlying mortality data. It is found that, for some countries, cohort dummies still need to be incorporated into the model. Moreover, when comparing the proposed model with well‐known mortality models in the literature, we find that our model provides comparable fitting but with a much smaller number of parameters. Based on 5‐year‐ahead mortality forecasts, it can be concluded that the proposed model improves the overall accuracy of the future mortality projection. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
87.
Genome-wide association studies of 14 agronomic traits in rice landraces   总被引:20,自引:0,他引:20  
Huang X  Wei X  Sang T  Zhao Q  Feng Q  Zhao Y  Li C  Zhu C  Lu T  Zhang Z  Li M  Fan D  Guo Y  Wang A  Wang L  Deng L  Li W  Lu Y  Weng Q  Liu K  Huang T  Zhou T  Jing Y  Li W  Lin Z  Buckler ES  Qian Q  Zhang QF  Li J  Han B 《Nature genetics》2010,42(11):961-967
Uncovering the genetic basis of agronomic traits in crop landraces that have adapted to various agro-climatic conditions is important to world food security. Here we have identified ~ 3.6 million SNPs by sequencing 517 rice landraces and constructed a high-density haplotype map of the rice genome using a novel data-imputation method. We performed genome-wide association studies (GWAS) for 14 agronomic traits in the population of Oryza sativa indica subspecies. The loci identified through GWAS explained ~ 36% of the phenotypic variance, on average. The peak signals at six loci were tied closely to previously identified genes. This study provides a fundamental resource for rice genetics research and breeding, and demonstrates that an approach integrating second-generation genome sequencing and GWAS can be used as a powerful complementary strategy to classical biparental cross-mapping for dissecting complex traits in rice.  相似文献   
88.
Walker-Warburg syndrome (WWS) is an autosomal recessive multisystem disorder characterized by complex eye and brain abnormalities with congenital muscular dystrophy (CMD) and aberrant a-dystroglycan glycosylation. Here we report mutations in the ISPD gene (encoding isoprenoid synthase domain containing) as the second most common cause of WWS. Bacterial IspD is a nucleotidyl transferase belonging to a large glycosyltransferase family, but the role of the orthologous protein in chordates is obscure to date, as this phylum does not have the corresponding non-mevalonate isoprenoid biosynthesis pathway. Knockdown of ispd in zebrafish recapitulates the human WWS phenotype with hydrocephalus, reduced eye size, muscle degeneration and hypoglycosylated a-dystroglycan. These results implicate ISPD in a-dystroglycan glycosylation in maintaining sarcolemma integrity in vertebrates.  相似文献   
89.
Loeys-Dietz syndrome (LDS) associates with a tissue signature for high transforming growth factor (TGF)-β signaling but is often caused by heterozygous mutations in genes encoding positive effectors of TGF-β signaling, including either subunit of the TGF-β receptor or SMAD3, thereby engendering controversy regarding the mechanism of disease. Here, we report heterozygous mutations or deletions in the gene encoding the TGF-β2 ligand for a phenotype within the LDS spectrum and show upregulation of TGF-β signaling in aortic tissue from affected individuals. Furthermore, haploinsufficient Tgfb2(+/-) mice have aortic root aneurysm and biochemical evidence of increased canonical and noncanonical TGF-β signaling. Mice that harbor both a mutant Marfan syndrome (MFS) allele (Fbn1(C1039G/+)) and Tgfb2 haploinsufficiency show increased TGF-β signaling and phenotypic worsening in association with normalization of TGF-β2 expression and high expression of TGF-β1. Taken together, these data support the hypothesis that compensatory autocrine and/or paracrine events contribute to the pathogenesis of TGF-β-mediated vasculopathies.  相似文献   
90.
Huang X  Zhao Y  Wei X  Li C  Wang A  Zhao Q  Li W  Guo Y  Deng L  Zhu C  Fan D  Lu Y  Weng Q  Liu K  Zhou T  Jing Y  Si L  Dong G  Huang T  Lu T  Feng Q  Qian Q  Li J  Han B 《Nature genetics》2012,44(1):32-39
A high-density haplotype map recently enabled a genome-wide association study (GWAS) in a population of indica subspecies of Chinese rice landraces. Here we extend this methodology to a larger and more diverse sample of 950 worldwide rice varieties, including the Oryza sativa indica and Oryza sativa japonica subspecies, to perform an additional GWAS. We identified a total of 32 new loci associated with flowering time and with ten grain-related traits, indicating that the larger sample increased the power to detect trait-associated variants using GWAS. To characterize various alleles and complex genetic variation, we developed an analytical framework for haplotype-based de novo assembly of the low-coverage sequencing data in rice. We identified candidate genes for 18 associated loci through detailed annotation. This study shows that the integrated approach of sequence-based GWAS and functional genome annotation has the potential to match complex traits to their causal polymorphisms in rice.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号